Differential sensors typically comprise at least two sensor elements positioned at two different locations on a substrate or in a package. Signals at the at least two sensor elements are subtracted to obtain a differential signal, or the difference between what is sensed at each sensor element. Examples of differential sensors include differential magnetic current sensors, differential wheel speed sensors, differential pressure sensors, and differential temperature sensors, among others.
Differential sensor output signals depend primarily on the physical quantity to be measured. For example, a differential Hall sensor responds to magnetic fields while a differential pressure sensor responds to pressure, etc. The change in the output signal versus a small change of input physical quantity is referred to as the sensor sensitivity (e.g., magnetic sensitivity, pressure sensitivity, etc.). This sensitivity also depends on mechanical stresses that act on the sensor elements. These stresses often relate to sensor package assembly, where various components with different coefficients of thermal expansion are joined together. These stresses can affect the various sensor elements unevenly, leading to inaccuracies and errors in the sensor output signal.
Conventional approaches include using special low-stress packages, with low-stress die attach and mold compound, and ceramic instead of plastic packaging, or attempting to compensate for the stress in each sensor element individually. These approaches, however, are inefficient, complicated and expensive, leading to higher sensor costs.
Therefore, there is a need for improved stress compensation in differential sensors.